"Geoffrey Barnes" wrote in message
link.net...

I'm guessing that the pressure differential at ground level isn't enough
to
prevent the exits from opening, but that this differential is (logically)
much higher at altitude, and thus would prevent the exits from opening in
flight. But I could be wrong.


The pressure differential wouldn't have to be that great to create a
considerable force holding the exit in place. I don't know what the surface
area of an exit is, but a square twenty inches on a side has an area of 400
square inches. It would take 200 pounds of force to overcome a 1/2 psi
pressure differential.